Cartel Land opens with the best shot of the whole documentary: thick white smoke billows and curls from plastic buckets, fading into the pitch-black desert night as a masked man explains the process through which the mixture in front of them becomes meth to be smuggled across the border.

He tells how they were taught the process by a father and son team from America: “those fuckers studied chemistry.”

It turns out that this clandestine reaction bubbling away before us is by quite some way the most straightforward and predictable happening in the film; if Cartel Land tells us anything it’s to reinforce the age old adage ‘everything is more complicated than it looks’.

The narrative is split between two groups, divided by 1,200 miles but united by a common antagonist in the shape of the Mexican drug cartels. We’re first introduced to Tim ‘Nailer’ Foley, a man of hard Southwestern grit who has made it his life’s work to push back against the gangsters and drug-runners he sees leaching across the border. Pacing the badlands, panting under the weight of his military-grade assault rifle, he cuts a troubling (and troubled) but still ineffably romantic figure in his lone stand against overwhelming odds. “I believe that what I am doing is good” he recites to the camera, and the swelling strings of Jackson Greenberg’s score more than suggest the Leone-esque undertones of the image.

The second half of the story concerns Dr. José Mireles, leader of the Autodefensas group down in Michoacán. Filled with a quietly irresistible charisma which seems no less diluted through the screen, loping through crowds with his black cowboy hat settled low on his head, he cuts quite the dashing figure.

Where Foley is something of a lone wolf, Mireles is very much the leader of a movement which rolls through Mexican towns driving out the cartels and gathering recruits as they go. “I hope they kick some ass down there,” Foley remarks as he watches news footage of his counterparts across the border, and as we get caught up in the ever-seductive narrative of a popular backlash against ruthless oppressors it’s hard not to cheer him on ourselves.

But of course things are never so simple. The Autodefensas command the lion’s share of screen time, and we watch as loyalties and mistrusts coil-in upon themselves while the movement grows ever larger and more unwieldy and attracts the attention of a government not overjoyed to see these people doing their job for them.

Just as the film portrays the violence of the pitched battles between the vigilantes and the cartels with impressive and at times shocking immediacy, so too does it refuse to shy away from the interpersonal complexities which make the situation so much more nuanced than simply ‘gangsters vs. good guys.’

Likewise the casual racism and reflexive defensiveness which characterises so many of the interactions with Foley and his posse makes it clear that these are hardly knights in shining armour (or even surplus store Kevlar).

The dual narrative works well, the switching back and forth between the isolated simplicity of Foley’s crusade and Mireles’ Babel of resistance ensuring that our attention is held without ever being exhausted. It does, however, leave little space for the real human cost of the war on drugs of which our characters are one of many facets. We are told early on, in a deeply affecting direct-to-camera account, of an atrocity committed by a cartel against a group of workers and their families, but this is the closest we ever get to the incredible emotional toll which this long struggle exacts upon the innocents caught in the middle.

Of course, harsh as it may sound, there is no shortage of material for those who want to see the horrors of this particular struggle on the ground. Heineman has rather given us a view of existence within the struggle; how people’s lives bend and warp around cartel activities like light around a black hole. With shots of Dr. Mireles treating children at his surgery or interviews with Foley describing his history of abuse and addiction, Cartel Land puts people – these particular people – at the heart of its concern. Then, with admirable bravery and candid access, it reminds us how little effect these people have on the terrible maelstrom into which they have been drawn.

Check out the rest of the latest cinema and streaming releases in our new movie reviews section, including the latest instalment in the Bourne franchise, Jason Bourne.